Roller press



Dec.17,1968 AHL ETAL 3,416,435

ROLLER PRESS Filed June 13, 1 966 2 Sheets-Sheet 1 INVENTOR. C'ar/ Ber/2 arm 00/;/

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Dec. 17, 1968 I QD ET AL 3,416,435

ROLLER PRESS Filed June 13, 1966 2 Sheets-Sheet z b 2 d a min a. 3 I'M l l \\F, \A. kw 00 v f C F m. a 1 m l r 1 8 3 w 6 .4 3 w 3 3 Cl/o //E I F2 -7 INVENTOR.

I 61 a, ,eemam Da// A e yaw c/ c/as/a-s 4* 4 'l r\ I )1 B Y TATTQRNEYS United States Patent 3,416,435 ROLLER PRESS Carl B. Dahl, Rockton, Ill., and Edgar J. Justus, Beloit, Wis., assignors to Beloit Corporation, Beloit, Wis., a corporation of Wisconsin Filed June 13, 1966, Ser. No. 557,111 8 Claims. (Cl. 100-170) ABSTRACT OF THE DISCLOSURE This invention relates to a press nip-defining device employing a pair of pressure load applying elements, preferably rolls, one of which consists of a rotary shell having a tendency to deflect in response to the load, which is subjected to rapid cyclic stress reversal in the shell annulus as it rotates, mounted on anti-deflection means, through load receiving to load relieving peripheral regions. For improved performance in such rapid cyclic stress reversal conditions the shell is formed of concentric integrated annular shell portions including outermost hard chill iron (Ni-Cr) alloy, innermost soft (low Ni-Cr alloy or substantially unalloyed) gray cast iron and intermediate (Ni-Cr content) mottled iron portions.

The instant invention relates to a load applying device and method, and more particularly, to a press nip-defining device including a roll shell and loading means of novel structure and arrangement, and a method of applying a generally uniform load at such press nip.

One aspect of the instant invention involves certain structures and methods wherein there is used a roll shell of substantial size not only in diameter but in a substantial length-to-diameter ratio. Such roll shell is centrifugally cast to form a chill iron alloy hard outer peripheral surface portion that is mounted on and carried by substantially 2 to 4 times its volume of primarily gray cast iron, which is poured, in the centrifugal casting process in a plurality of separate pours, preferably only two, such that the first pour of essentially gray cast iron against the inner periphery of the hard chill iron shell portion will effectively wash only a relatively nominal amount of alloying material out of the previously poured chill iron shell portion, and such initial essentially gray cast iron pour will thus have a mottled iron metallurgical structure, with certain hard components therein resulting from alloying elements which may be picked up by the first essentially gray cast iron pour. The second essentially gray cast iron pour, however, will be substantially effectively precluded from picking up any significant amount of hard alloying components because of the previous pour, and as a consequence the second gray cast iron pour will function effectively as a soft iron innermost shell portion which can be readily machined and on which the various shell mounting means may be afiixed with considerable advantage, because of the substantially complete absence of any localized hard spots (i.e., containing anything more than nominal trace amounts of Ni-Cr hard alloying elements) in the innermost gray cast iron shell portion. In addition, such triple pour shell affords the advantage of retaining the hard and comparatively unyielding outer peripheral chill iron portion in a condition of substantial axial as well as circumferential compression. By effectively precluding a condition wherein the chill iron outer shell portion may be subjected to tension, it is found that the instant pressure roll shells have substantially greater life than could heretofore be obtained in the case of many prior art rolls.

In the instant invention, a press nip-defining device is provided which comprises a first pressure applying ele- Patented Dec. 17, 1968 ment or roll and a second pressure roll in press nip-defining relation therewith. Such second pressure roll is provided with the shell hereinbefore described, and it is also provided with anti-deflection means of numerous types, heretofore known and used with other roll shells. Additionally, the instant invention provides a method for applying a generally uniform load along a press nip line by the use of the instant shell and by the use of fluid pressure loading means acting against the inner periphery of the shell opposite the nip to load the shell and at the same time relieve any pressure against the inner periphery of the shell opposite to that portion loaded against the nip. In this way the shell undergoes a rapid cyclic stress reversal during rotation, but the metallurgical characteristics of the shell, plus the manner in which forces are applied to the hard chill iron outer periphery thereof during such cyclic stress reversal, make possible superior load application and handling.

Other and further objects, features and advantages of the present invention will become apparent to those skilled in the art from the following detailed disclosure thereof and the drawings attached hereto.

On the drawings:

FIGURE 1 is an essentially schematic elevational view of a roll shell of the invention mounted for rotation on conventional mounting means;

FIGURE 2 is a cross sectional view taken substantially along the line II-II of FIGURE 1, showing schematically and somewhat enlarged from the view of FIGURE 1 the relative relationship of the various concentric portions of the shell;

FIGURE 3 is a fragmentary enlarged essentially schematic view which is a cross sectional view taken substantially along the line III-III of FIGURE 2;

FIGURE 4 is an essentially schematic elevational view of a calendar stack employing the roll shell in a pressure loading device embodying the instant invention;

FIGURE 5 is an essentially schematic elevational view, with parts broken away and shown in section, of a pair of rolls defining a press nip embodying the instant invention;

FIGURE 6 is a schematic elevational view, with parts broken away and parts shown in section, and schematically represented, showing a pair of press rolls defining a press couple embodying the instant invention; and

FIGURE 7 is an essentially diagrammatic representation of loads and forces applied in the arrangement of FIGURE 6.

As shown on the drawings:

A press roll mounting indicated generally by the reference numeral 10, is shown comprising a press roll shell indicated generally by the reference numeral 11. The shell 1.1 is rotatable about its centroidal axis C and is represented as having an axial length L. At opposite ends thereof heads 13 and 14 are secured by bolts, indicated at B, B and the heads 13 and 14 mount stub shafts 15 and 16 which are in turn carried by anti-friction means, in the form of diagrammatic representations of bearings at 17 and 18 mounted on fixed structures F, F. The shell 11 is also shown in cross section in FIGURE 2 as being composed of an outermost hard chill iron alloy shell portion 11a, an innermost soft low alloy (or substantially unalloyed) gray cast iron shell portion 11b and an intermediate substantially mottled iron shell portion 110. The intermediate shell portion 11c is secured (in substantially rigid assembly) substantially coextensively with the outer and inner shell portions 11a and 11b by metallurgical bonds at 11d and 112, respectively. The shell 11 is shown as having a diameter D (outside diameter) and an annular composite or total radius of the integrated shell portions 11a through He of a dimension R.

In the particular uses contemplated for the instant invention, the shells 11 centrifugally cast are of substantial magnitude in outer diameter D (i.e. perhaps 1 to 4 or 5 feet) as well as annular radial dimension R (eg 2 to 6, 8 or even 12 inches, depending upon the outer diameter D as well as the overall axial length R, and perhaps better expressed in terms of ranges from substantially to substantially of such outer diameter D). It will also be appreciated that the axial dimension is'coinparable to that of paper making machinery crossmachine dimensions, e.g., a practical minimum in the neighborhood of about 100 inches to approximately the present-day maximum in the neighborhood of substantially 400 inches. Again, the diameter D and axial length L are better expressed in terms of the socalled length-todiameter ratio, which is substantial in any event and is within substantially a practical range of about 4:1 to 15:1.

In addition, it would be appreciated that the essential chemical compositions of the shell portions 11a, 11b and 11c are substantially as follows:

The outermost shell portion 11a is formed of substantially Percent Ni 1.4 to 1.7 Cr 1.9 to 2.2 C 3.6 to 3.8 Si 0.4 to 0 .5

remainder substantially Fe, with incidental impurities; the innermost shell portion 11b is formed of substantially Percent Ni 0.02 Cr 0.02 C 3.0 to 3.5 Si 2.0 to 2.9

remainder substantially Fe; with incidental impurities; and the intermediate shell portion 11c has substantially an overall mottled iron composition containing on the average substantially Percent Ni At least 0.02 to 0.05 Cr At least 0.02 to 0.05

remainder substantially the gray cast iron composition specified herein for the innermost shell portion 11b. In actual practice, it is generally preferable to employ a total volume of gray cast iron in the two pours for the intermediate and innermost shell portions 110 and 1.117, respectively, that is substantially 2 to 4 times the total volume of the outermost chill iron alloy volume. As indicated, in FIGURE 3, it will be noted that the outermost chill iron alloy portion 11a is indicated as having a radial dimension R and the overall radial dimension is indicated at R for the combination of the two successive intermediate and innermost annular portions 110 and 1111, respectively. Such composite radial dimension R is shown to be substantially greater than R but actually the view is essentially schematic and the radial dimension R is even greater in proportion than R in actual practice. Shown also in exaggerated size are the two metallurgical bonds 11d and 11e. Actually, in the finally poured shell 11, after it has been machined and polished smooth at its ends, so-called ghost lines can be seen in the region of the metallurgical bonds 11d and 11e, but not in the comparative exaggeration of the sizes shown in the schematic view of FIGURE 3, even though such ghost lines are quite visible with proper polishing.

In making the centrifugally cast shell 11 hereof, an appropriate permanent .mold having a metal shell and appropriate mold Wash therein or a sand lined mold can be used. In a typical pouring operation, a sand lined mold is used and the sand is positioned therein in conventional manner, and then heated to dry the same before pouring. In general, pouring techniques are explained in Krepps U.S. Patent No. 2,710,997 and Samuels US.

Patent No. 2,964,251. The initial molten iron alloy having a ladle composition substantially as that just specfied for the ultimately poured outermost shell portion 11a is then poured into the sand mold which is being rotated so as to effectively form an annular molten body of substantially uniform radius R which is permitted to cool relatively rapidly i.e., to chill at a rate sufficient to effect formation of said hard chill iron alloy via the presence of substantially 3.3 to 3.9% total Ni-Cr alloying elements (in Ni:Cr weight ratios of substantially 1.4 to 1.7:l.9 to 2.2) in the relatively high C and low Si iron composition herein specified. The aforesaid prior art patents suggest that the second pour should be made while the first poured metal is still in a plastic or mushy condition, but it is sufficiently important in the practice of the instant invention to avoid washing out too much of the alloy components from the first pour when the second pour is made so that the first pour is permitted to cool somewhat more than is recited in the prior art patents, and an appropriate flux is applied in small amounts to the inner surface of the first pour (at, for example, L of FIGURE 3), so that there will be a better metallurgical bond 11d formed between the first and second pours 11a and 110, respectively. In a typical case substantially 9000 pounds of metal are poured in the first pour 11a and substantially 9000 pounds of gray cast iron are poured in this manner in the second pour (again indicated schematically at on FIGURE 3). The second pour (also substantially 9000 pounds in this example) has a ladle composition that is substantially that hereinbefore specified for the innermost gray cast iron shell portion 11b, but the pouring of the second pour to make the intermediate shell portion 110 not only results in re-heating, via the flux for the formation of an effective metallurgical bond at 11d, but also results in a washing out of a certain amount of the nickel and chromium alloy components of the chill iron alloy and incorporating of the same in a mottled iron resultant intermediate shell portion 11c, wherein the overall nickel and chromium proportions are found to be substantially at least above trace amounts of less than 0.02% and may be described as being substantially at least about 0.02 to 0.05% nickel and substantially at least about 0.02 to 0.05% chromium. The metallurgical bond 11d indicated schematically is essentially a composite mottled iron very thin layer (here shown in exaggerated size) which is functionally an extension of the metallurgy of the outer shell portion 1.1a merged with an extension (metallurgically) of the intermediate shell portion 110, in such a way that the presence of this so-called merging of the two metallurgies is in the form of a visible ghost line when viewed on a polished end of the roll, suggesting that there is really an additional mottled iron composition intermediate the innermost chill iron periphery indicated at L and the outermost intermediate shell portion periphery indicated at L and having a distinct radial dimension shown in exaggerated size at R although the ghost marking actually visible does have a noticeable radial dimension. Without describing in substantial detail, it will be appreciated that when the third pour of gray cast iron is made to form the innermost shell portion 11b, it is also poured after the intermediate pour has had an opportunity to cool somewhat longer than the prior art suggests, but again with application of flux (which is disclosed in the prior art) in order to effect the required secure metallurgical bond here shown diagrammatically at 11e.

Metallurgists will recognize the herein described concepts of obtaining or avoiding, selectively, the hard chill iron alloy formation by the correlating of cooling rates with relative Ni, Cr, Si and C contents; but the invention resides in claimed structural environment demonstrating the unique advantages obtained in satisfying a long recognized but unfilled need.

When the shell 11 is poured, through the triple pour procedure, and cooled sufliciently, it is then removed from the sand mold and it is necessary to machine down the outer surface to obtain a smooth pressure surface indicated at P in FIGURES 2 and 3, and a certain nominal amount of smoothing of the inner surface, i.e., the innermost peripheral surface IP is also carried out. It will be appreciated that the gray cast iron innermost shell portion 11b is soft and is readily machined not only for purposes of smoothing the inner peripheral portion IP thereof, but also for purposes of making whatever connections may be required for heads for mounting the shell 1.1 and so forth. Thus, the matchining of bolt holes for the bolts B indicated in FIGURE 1 is easily carried out using the gray cast iron inner shell portion 11b. In addition, the substanial additional volume of 2 to 4 times the chill iron alloy volume that is used for the total of the gray cast iron pours (i.e., in the previous example using 9000 pounds for the first gray cast iron pour to make the intermediate shell portion, one uses approximately 18,000 pounds of gray cast iron to complete the third pour to form the innermost gray cast iron shell portion 11b), it

is found that the substantial additional body of gray cast iron has the effect of holding and securely retaining the chill iron alloy outer shell portion 11a in compression. The chill iron alloy will shrink substantially as it hardens in the initial pour, and the two successive gray cast iron pours will in each instance form the metallurgical bonds and then with continued cooling, which takes place, sequentially, after the bulk of the shrinkage has occurred in the chill iron alloy layer 1111, results in the application of substantial compressive forces to the chill iron alloy via the intermediate and inner shell portions 110 and 11b, by virtue of the metallurgical bonds 11d and 112, respectively. This compression applied to the chill iron alloy shell portion 11a is not only axial compression but it is also circumferential compression, such that the chill iron alloy shell may retain its hardness and at the same time will not be subjected to tension forces during its functioning as a load carrying medium. The chill iron alloy shell portion 11a is extremely effective as a hard nip-defining pressure surface P bearing element 11a, but it is not of the type of metallurgy that withstands tension forces satisfactorily. The sequential nature of the triple pour here involved, thus assures an extremely desirable compression load on this outer shell portion 11a.

Referring briefly to FIGURE 5, it will be seen that there is shown a top press nip-defining roll 20 which is provided with load applying means, here shown only schematically as the double headed arrow A, but understood in the art to involve conventional press nip load applying means in the form of fluid pressure actuated diaphragms or the like acting upon bearings mounting the press roll 24 rotation. In FIGURE 4, it will be seen that in the calender stack a bottom roll 11B mounts and bears substantially the weight of the superimposed upper rolls 21, 22, 23, 24, 25 and 26, in a typical calender arrangement for load application at a calender nip N-C with the bottom roll 11B. In FIGURE 5 the bottom roll 11C is in position to define a press nip N with the top roll 20 along a nip line NL which like the nip line NL at the nip NC of FIGURE 4 extends in the cross-machine direction and can only be viewed as a point in FIGURES 4 and 5. In FIGURE 6, it will be seen that the nip line NL is represented as extending in the cross-machine direction and is represented as being loaded by a plurality of downwardly directed arrows, indicating a generally uniform load being applied generally normal to the nip line NL between an upper press roll 30 and a lower press roll 11d. It will be noted that the upper press roll 30 is shown with stub shafts 31 and 32 which are conventionally mounted in bearings to afford rotation for the upper press roll 30, and the bearings are loaded, as indicated at PL, by the load applying means which load against the stub shafts 31 and 32 through the respective bearings 31b and 32b so as to afford uniform distribution of the load along the 6 load line NL as indicated schematically by the plurality of downwardly directed arrows.

The bottom roll 11d, like the rolls 11c and 11b, has the same triple pour composite structure already described in connection with the shell 11. Thus, the shell 11d is composed'of an outer chill iron alloy shell 11D, an inner gray cast iron shell portion 11Db and an intermediate mottled iron portion 11Dc, as shown. In addition, it will be seen that the shell 11D carries sleeved heads 38, 39 which rotate with the shell 11D on bearings 36 and 37 carried by stub shaft-like extensions 34 and 35 which actually are held against rotation and extend within the shell 11D to carry means for selective fluid pressure application which are actually the same as those shown schematically in the cross sectional view of the roll B of FIGURE 4. The shell for the roll 11B is rotatably mounted about a core C-4 which carries seal-s S-4 and S4a-aff0rding a seal between the core C-4 and the inner periphery of the shell indicated at 11' for the roll 11B, so as to seal off a fluid pressure area FP-A for fluid pressure to act against the inner periphery of the shell 11' substantially opposite the nip line NL of FIGURE 4, or as shown as fluid pressure FP in dotted line arrows acting against the inner periphery MD!) in FIGURE 6, in substantial opposition to the solid line downwardly directed arrows representing the uniform load applied to the top of the nip line NL in FIGURE 6. The structure shown in FIGURES 4 and 6 for the rolls 11B and 11D is essentially that shown in Wilsdon British Patent No. 641,466.

In contrast, the view of the shell 11" for the roll 11C (which shell 11" has the same composite structure hereinbefore described) shows that the shell is mounted to receive a stationary core C-5 having a generally axially extending slot S-S extending substantially coextensive with the nip load line NL and carrying a piston of comparable length and shape indicated at P-5, which is loaded from beneath at the fluid pressure chamber FP5 in the bottom of the slot S-5 and which acts against a coextensive free pivot rod R-S pivotally mounting a shoe RS5 presenting a substantially rigid face to the inner periphery of the shell 11" for effectively holding an oil film or generating a hydraulic wedge in an oil film through which the fluid pressure load is exerted and urged against the inner shell periphery. The essentially schematic view of FIGURE 5 is more fully described in E. J. Justus Patent No. 3,276,- 102, which disclosure is incorporated herein by reference.

As the load diagram of FIGURE 7 indicates the chilled alloy iron outer shell 11Ea is shown in section carried by the composite inner gray cast iron portions 11E (which are representative of previously described intermediate 11c and inner 11b shell portions. The compressive load is indicated by the opposed arrows CL, which compressive load is initially developed with the cooling of the intermediate and inner shell portion pours and with the cooling thereof, which takes place at least partially after the substantial shrinkage and cooling of the chill iron alloy outer shell portion 11Ea. Thus, the outer shell portion 11Ea is maintained under compression by a substantial body or bulk of material represented herein as 11E. The circumferential compression is, of course, applied similarly. The essential concept herein being that if a load in a local area LL were to develop even temporarily it is possible that a nominal deflection could develop in the chill iron alloy shell portion as indicated by the dotted lines at 11E'a, and this nominal deflection in the outer shell portion 11Ea would effect an axial dimension increase therein, at least theoretically, and it is the essential function of the greater volume and overall resultant strength of the softer intermediate and inner shell portions 11E to continuously maintain this compressive load CL on the chill iron alloy outer peripheral shell portion 11Ea so that at least the first or initial deflection of the type just mentioned will really only relieve some of the compression rather than exert tension forces on the chill iron alloy. Likewise, if the fluid pressure is sufficientto correct tendencies toward downward deflection in the force diagram of FIGURE 7, it will, of necessity, be sufiicient to actually effect some upward deflection if the top nip loading device pressing down against the nip load line NL should be momentarily relieved, then there might be an upward deflection of a very nominal extent in the outer chill iron alloy portion 11Ea along the nip line NL but again this tendency toward deflection is generally only such as to relieve some compression on the chill iron alloy layer rather than actually subject the layer or shell portion 11Ea to tension. On the other hand, it is appreciated that the opposed loads along the nip line NL are substantial, whereas loads at the opposite region or limited circumferential area portion of the shell are substantially completely relieved in the case of each of the various fluid pressure loading devices hereinbefore disclosed. This means that the shell itself, as it rotates, must go through the region in the neighborhood of the nip load line NL- whereat it is subjected to substantial opposed forces (either one of which alone can probably effect a certain amount of deflection in the roll shell, but which in opposition tend to minimize such deflection), whereupon at the underside of the shell there is an opposed region of no stress or no load applied to the shell in any significant extent. There is thus a cyclic stress reversal continuously taking place in the rotating loaded roll. By the use of the instant arrangement and overall shell structure incorporated therein (particularly that maintaining the chill iron alloy outer shell portion in substantial compression) it is possible to subject the instant roll to such rapid cyclic stress reversals for substantial periods of time without effecting any metallurgical changes in the various distinct inner portions of the roll and/or any undesirable creation of physical defects therein.

It will also be appreciated that there are a substantial number of other anti-deflection means or devices known in the art, which may also be used to advantage with the instant shells in the loaded nips, calenders, or similar devices involving the loading of such shells.

In this respect the uses contemplated are too numerous to describe in detail, but characteristic uses of such shells are best described by reference to already issued prior art patents showing machinery wherein such shells are used in so-called anti-deflection mountings characterized therein or the mountings described wherein serious problems in the correction of operating deflection characteristics of roll shells are purported to be answered, by internal and/ or external reinforcement, internal filling, internal and/or external application of forces at specific operating regions or points and/or via the application of characteristic forces referred to as force couples in such disclosures. Typical patent disclosures of the type just described include:

US. Patent No.

It will be understood that modifications and variations may be effected without departing from the spirit and scope of the novel concepts of the present invention.

We claim as our invention:

1. In a device for defining a press nip for pressure application to longitudinally traveling material along a transversely extending nip line defined on a first transverse element presenting a surface for applying a substantially uniform load along such line generally normal to nip line, the improvement of a second transverse element mounted in opposed nip-defining relationship with such first element and generally coextensively with such transversely extending line, such second element comprising a rotary roll shell of substantial axial length-to-diameter having a tendency to deflect in response to such load application of the first element along the nip line and anti-deflection means operatively connected to such shell for effecting substantially uniform load application at the nip and substantially counteracting such tendency to deflect by application of substantial forces to a first peripheral shell region receiving such load along the nip line with accompanying substantial relief force application to a second peripheral shell region circumferentially opposite to said first portion and transversely coextensive therewith, thereby elfecting rapid cyclic stress reversal in the shell annulus, said shell consisting essentially of a plurality of concentric integrated annular shell portions including an outermost hard chill iron alloy, an innermost soft low alloy gray cast iron and an intermediate mottled iron shell portion effecting coextensive secure metallurgical bonds with the outermost and innermost shell portions, each of such shell portions having a substantially uniform annular radial dimension throughout the shell length, such intermediate and innermost shell portions having a total volume of substantially 2 to 4 times that of the outermost shell portion and effectively maintaining such outermost shell portion in substantial axial and circumferential compression during the aforesaid rapid stress reversal cycle, whereby superior retention of load-bearing characteristics of the shell is obtained during rapid cyclic stress reversal operations, said outermost shell portion being formed of substantially Percent Ni 1.4 to 1.7 Cr 1.9 to 2.2 C 3.6 to 3.8 Si 0.4 to 0.5

remainder substantially Fe, with incidental impurities; said innermost shell portion being formed of substantially remainder substantially Fe, with incidental impurities; and said intermediate shell portion having substantially an overall mottled iron composition containing on the average substantially Percent Ni At least 0.02 to 0.05 Cr At least 0.02 to 0.05

remainder substantially the gray cast iron composition specified herein for the innermost shell portion.

2. The device of claim 1 wherein said anti-deflection means include means for maintaining substantially uniform fluid pressure along a circumferentailly limited area on the inner shell periphery at said first shell region and substantially coextensively with such nip line while relieving fluid pressure against the shell at said second shell region.

3. The device of claim 2 wherein such fluid pressure is applied against an elongated flexible element presenting a hard surface to the innermost shell periphery and loading via an oil film on such hard surface against the shell periphery for indirect substantially uniform load application via such fluid pressure against the shell coextensive with such nip line.

4. The device of claim 3 wherein the radical dimension of the composite shell annulus is substantially /3 to A of the shell diameter.

5. A device for defining a press nip for receiving and pressing longitudinally traveling sheet material, which comprises a first rotary roll, a second rotary roll in nip-defining relationship with the press roll of receiving and pressing therebetween such traveling sheet along a transversely extending nip line, load-applying means operatively associated with said first roll for load application of the same generally uniformly against the second roll along such nip line, such second roll comprising a rotary roll shell of substantial axial length-to-diameter having a tendency to deflect in response to such load application and anti-deflection means operatively connected to such shell for effecting substantially uniform load application at the nip and substantially counteracting such tendency to deflect by application of substantial forces to a first peripheral shell region receiving such load along the nip line with accompanying substantial relief of force application to a second peripheral shell region circumferentially opposite to said first portion and transversely coextensive therewith, thereby effecting rapid cyclic stress reversal in the shell annulus, said shell consisting essentially of a plurality of concentric integrated annular shell portions including an outermost hard chill iron alloy, an innermost soft low alloy gray cast iron and an intermediate mottled iron shell portion effecting coextensive secure metallurgical bonds with the outermost and innermost shell portions, each of such shell portions having a substantially uniform annular radial dimension throughout the shell length, such intermediate and innermost shell portions having a total volume of substantially 2 to 4 times that of the outermost shell portion and effectively maintaining such outermost shell porion in substantial axial and circumferential compression during the aforesaid rapid stress reversal cycle, whereby superior retention of load-bearing characteristics of the shell is obtained during rapid cyclic stress reversal operations, said outermost shell portion being iron alloy formed of a low substantially 0.4 to 0.5% Si content with substantially 3.3 to 3.9% total effective content of Ni-Cr hard shell alloying elements, in NizCr weight ratios of substantially 1.4 to 1.7: 1.9 to 2.2, in an iron composition of substantially 3.6 to 3.8% C, remainder substantially Fe, with incidental impurities; said innermost shell portion being gray iron formed of substantially not more than nominal trace Ni-Cr hard alloying elements in combination with an effectively soft iron forming substantially 2.0 to 2.9% Si content, in an iron composition of substantially 3.0 to 3.5 C, remainder substantially Fe, with incidental impurities; and said intermediate shell portion having substantially an overall mottled iron composition containing on the aver-age substantially Ni-Cr contents intermediate those of said outermost and innermost shell portion, substantially in the form of localized spots of more than said nominal trace amounts of Ni-Cr hard alloying elements in a matrix forming the remainder of substantially the gray cast iron composition specified herein for the innermost shell portions of substantially 2.0 to 2.9% Si, 3.0 to 3.5% C, remainder substantially Fe with incidental impurities.

6. The device of claim 5 wherein said anti-deflection means include means for maintaining substantially uniform fluid pressure along a circumferentially limited area on the inner shell periphery at said first shell region and substantailly coextensively with such nip line while relieving fluid pressure against the shell at said second shell region.

7. The device of claim 6 wherein such fluid pressure is applied against an elongated flexible element presenting a hard surface to the innermost shell periphery and loading via an oil film on such hard surface against the shell periphery for indirect substantially uniform load application via such fluid pressure against the shell coextensive with such nip line.

8. The device of claim 7 wherein the radial dimension of the composite shell annulus is substantially /3 to A of the shell diameter.

References Cited UNITED STATES PATENTS 288,176 11/1883 Harris et al 29148.4 3 99,295 3 1889 Totten 29-1 10 2,030,891 2/ 1936 Payne 29148.4 2,097,709 11/ 1937 Walters 241293 X 2,710,997 6/1955 K-repps 16467 2,812,571 11/1957 Strom 29130 2,964,251 12/ 1960 Samuels et al. 241-293 3,119,324 1/1964 Justus 29116 X 3,146,160 8/ 1964 Kaakaanpaa 162-305 LOUIS O. MAASSEL, Primary Examiner.

.U.S. Cl. X.R. 

